I am sceptical, I'm afraid. Tecoma capensis is a vigorous perennial which grows into a pretty large vine. A couple of them would fill that whole bed if I have understood the scale right. I don't see how a planter attached to the fence could supply sufficient growing medium and nutrients for it. Plus it would have to be watered constantly. It could even bring a wooden fence down I should think. Is there a reason you can't plant them at the bottom of the fence and let them grow up, from where they will then hang down?

Thanks for the info. This area of the yard is slightly slanted for drainage. It's never held water but I'm afraid if we get too much rain it might kill the plants. I would love to just plant in the ground if possible. I'm wanting honeysuckle but now I may rethink it. Maybe something lighter growing on a trellis.